1. Field of the Invention
The present invention relates to a method and an apparatus for processing composite geometric object data represented by combinations of a plurality of geometric elements to display the object, and to a computer readable storage medium storing programs which a computer executes to realize such geometric object data processing and displaying.
2. Description of the Related Art
A geometric object is generally represented by a plurality of sets of geometric elements such as lines having some width and faces or planes having some size. A face is painted with color in some cases. Direct processing of data of geometric element sets of a complicated geometric object is not so simple, so that geometric elements are generally divided into groups by using various indices.
Geometric objects include a two-dimensional geometric object defined on one plane such as a flat plane and a three-dimensional geometric object defined in a three-dimensional space. A three-dimensional geometric object is often displayed by projecting it on a tow-dimensional plane because a general display device has only a two-dimensional display screen.
Grouping geometric elements into units of part or component which is the basic unit capable of being disassembled or removed is often performed, particularly when an object is displayed by using a plurality of geometric elements. Namely, with this grouping method, one part is represented by a set of lines and faces, of only lines, or of only faces which constitute one group. The configuration of an object is therefore displayed by these sets, i.e., a plurality of groups of geometric elements.
Computer aided design (CAD) systems used in engineering fields are typical examples with which geometric objects are displayed by the above-described method. Main objects to be displayed are industrial products each of whose configuration is displayed by a plurality of groups each constituting one geometric object or part which is the basic unit capable of being assembled or disassembled.
For the display processing of grouped geometric data, the geometric data in a storage medium is read and processed in the sequential order of groups. Namely, after a geometric object belonging to group A is displayed completely, a geometric object belonging to group B is displayed, and so on.
Users desire that a (composite) geometric object should be displayed as fast as possible to quickly grasp the outline thereof. In order to satisfy this requirement, the following approaches have been performed in addition to simply speeding up the display processing speed.
A first approach is to progressively display a geometric object each time data is read, each time data is received via a communications line, or each time a display pre-process is performed. With this approach, a user possibly grasps the outline of a geometric object at an earlier stage when a fraction of the geometric object is displayed. This possibility is particularly high when a user judges from a partially displayed geometric object whether it is a desired one among a plurality of geometric objects. Therefore, the user can make judgement in a short time without waiting for the input and display of all data of each geometric object. This approach is also effective for changing the position and direction of display, from the same reason as above.
A second approach is to display each geometric object sequentially starting from a larger size object. Generally, a large size geometric object plays an important role in grasping the outline of a final geometric object constituted of a plurality of geometric objects. A system for realizing this approach is constituted of, as shown in FIG. 3, an input unit 101, a computing unit 102 and an output unit 103. The input unit 101 reads geometric data sets of a display object. The order of reading the geometric data sets is not limitative. The computing unit 102 has a sequence scheduling unit 202 which schedules the order of displaying faces of a display object in such a manner that each face is displayed in the order of larger area size. The output unit 103 displays data of each face in the scheduled order.
As shown in FIG. 5, the output unit 103 may output the scheduled geometric data to a storage unit 501 or a communications apparatus, and a display unit 502 displays the scheduled geometric data stored in the storage unit 501 or sent from the communications apparatus.
Apparatuses and methods for realizing the above approaches are disclosed in "Developments on Three-dimensional Data Viewer GhostSpace" by Daisuke, NISHIOKA and Mikio NAGASAWA, Information Processing Society of Japan, Papers of Multimedia Communications and Distributed Processing Workshop, pp. 261-266 (1996). The contents generally the same as above are disclosed in Technical Information provided by Ultra-high Speed Network and Computer Technology Laboratories (UNCL) on the Internet (http://www.iijnet.or.jp/uncl/GhostSpace/technotej.html) as of Nov. 25, 1996, and in U.S. Pat. No. 4,994,989 and U.S. Pat. No. 5,379,371.
There are apparatuses applying such technologies which apparatuses are provided with a means for receiving a user instruction while a geometric object is displayed, identifying a geometric object corresponding to the user instruction or a group the geometric object belongs to, and displaying attribute data of the geometric object or group. Many CAD systems use these technologies to provide a function of displaying the attribute data of a part in response to a designation of the part.
There is also a means for displaying a progress of how far the process such as data input advances, by using a one-dimensional bar graph. For example, computer software, word processor MS-WORD (trade name) of Microsoft Corp., displays a progress state of a data read or save process.
Conventional technologies of the above-described two approaches are, however, not satisfactory in that they consider grouped geometric data processing not so much. Specifically, although geometric data is grouped, each face (geometric element) constituting the geometric object is simply displayed in the order of larger area size, without positively utilizing the characteristics of grouping.
Therefore, if the configuration of a composite geometric object such as a mechanical apparatus is displayed as a set of geometric elements in the unit of face simply in the order of larger area size, then a small part having a narrow area size is displayed only near at the last stage of the display process.
In the case of a composite geometric object such as a mechanical apparatus, the configuration as well as a presence/absence of each part becomes important when the outline of a final geometric object is grasped. It is therefore preferable to display an independent part at an earlier stage even if it is small in size. This is particularly preferable when a process is to be performed in response to a designation of a part made for the display of attribute data such as material and manufacturer other than for the display of the configuration. With conventional apparatuses and methods, however, a small part is not displayed until the near final stage of the display process, so that an earlier designation of a small part is not possible. A composite geometric object such as a mechanical apparatus is generally grouped in the unit of part, for the convenience of data management and the like.
The above problem is also associated with wire-frame (line drawing) representation of a geometric object.
The conventional display method of displaying each face in the order of larger area size may be associated with another display method of displaying a geometric object in the order of group size, e.g., in the order of volume size. Also with this method, it is obvious that a small part is displayed later, and the above problem cannot be solved.
The outline of geometric objects occupying a large space, such as buildings and a row of houses on a street, can be grasped at an earlier stage if a near geometric object is displayed with a priority over a far geometric object. The outline can be grasped at a much earlier stage if a larger geometric element is displayed preferentially in addition to the preferential display of a near geometric element. However, geometric object display methods and apparatuses have not been proposed to date which can display each geometric element in the priority order thereof, independently from a geometric group such as each building and each room.
Only a one-dimensional display means has been proposed for the display of a progress state of a display process. Therefore, for example, while a plurality of parts are displayed, it is not possible to display how far the process of displaying each part is advanced.